The demonstrators blocked balloting in a fifth of the country's constituencies and say Yingluck must resign and make way for an appointed "people's council" to overhaul a political system they say has been taken hostage by her billionaire brother and former premier, Thaksin Shinawatra.
Sunday's election, which the main opposition party boycotted, is almost certain to return Yingluck to power and with voting passing off peacefully across the north and northeast, Yingluck's supporters will no doubt claim a legitimate mandate.
But the vote is unlikely to change the dysfunctional status quo in a country popular among tourists and investors yet blighted by eight years of polarization and turmoil, pitting the Bangkok-based middle class and royalist establishment against the mostly poor, rural supporters of the Shinawatras, Reuters reported.
Apart from a few scuffles, the election was peaceful, with no repeat of the chaos seen the previous day, when supporters and opponents of Yingluck clashed in north Bangkok, with seven wounded by gunshots or explosions.
Voting was disrupted in 18 percent of constituencies, 69 out of 375, nationwide, the Election Commission said, affecting 18 of 77 provinces. Neither the result nor the turnout were announced.
The disruptions mean it could be weeks before parliamentary seats are filled, so Yingluck will remain a caretaker with no policy authority.